With each successive semiconductor technology generation, diameters of substrates, e.g., wafers, tend to increase and transistor sizes decrease, resulting in the need for an ever higher degree of accuracy and repeatability in substrate processing. Semiconductor substrate materials, such as silicon substrates, are processed by techniques which include the use of vacuum chambers. These techniques include non plasma applications such as electron beam deposition, as well as plasma applications, such as sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), resist strip, and plasma etch.
Plasma etching systems available today are among those semiconductor fabrication tools which are subject to an increasing need for improved accuracy and repeatability. One metric for plasma etching systems is increased uniformity, which includes uniformity of process results on a semiconductor substrate surface as well as uniformity of process results of a succession of substrates processed with nominally the same input parameters. Continuous improvement of within-substrate uniformity is desirable. Among other things, this calls for plasma chambers with improved uniformity, consistency and self diagnostics.